In a microwave semiconductor amplifying element, high efficiency operation can be achieved when the load impedance for the second harmonic seen from the output electrode end of the semiconductor amplifying element is made near-open.
In this case, it is assumed that the load impedance for the second harmonic signal seen from the output end part of the package is e.g. approximately 50Ω or more. Here, the term “approximately 50Ω” means 47Ω or more and 53Ω or less.
However, when a bias circuit is provided between the output matching circuit and the external load, the load impedance for almost part of the second harmonic signal seen from the output end part of the package may fall below 50Ω. This may decrease the efficiency.